[PATCH 0/1] use RT_PROPERTIES table to implement efi=novamap

[Ard Biesheuvel]

This patch addresses an oversight on my part when I implemented Linux
side support for the EFI RT properties table: SetVirtualAddressMap() is
itself a runtime service which is only callable at runtime to begin with,
and so the EFI stub should only call it if it is not marked as unsupported.

This may be useful for the Snapdragon EFI based laptops, which already rely
on a special EFI driver to expose the correct DT based on metadata exposed
by EFI. These systems ship with a broken implementation of SetVirtualAddressMap,
which is currently being worked around by passing efi=novamap on the kernel.
command line.

After applying this patch (which I intend to propose for backporting to 5.10),
the same can be achieved by exposing a RT_PROP table that marks SetVAMap() as
unsupported. And while at it, better mark the variable services as unsupported
as well, since they don't work under Linux either.

I'm open to extending this with a Linux specific override value kept in a
EFI variable, so that platforms that cannot support DtbLoader are able to
implement something similar.

Cc: Jeffrey Hugo <jhugo at codeaurora.org>,
Cc: Bjorn Andersson <bjorn.andersson at linaro.org>
Cc: Shawn Guo <shawn.guo at linaro.org>
Cc: Rob Clark <robdclark at gmail.com>
Cc: Leif Lindholm <leif at nuviainc.com>
Cc: linux-arm-msm at vger.kernel.org

Ard Biesheuvel (1):
  efi: stub: omit SetVirtualAddressMap() if marked unsupported in
    RT_PROP table

 drivers/firmware/efi/libstub/efi-stub.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

-- 
2.30.1